Scientists find gamma ray halo around Milky Way
November 4, 1997
Web posted at: 11:53 p.m. EST (0453 GMT)
WASHINGTON (Reuters) -- A vast halo of gamma rays surrounds
the Milky Way galaxy, scientists reported Tuesday, but they
don't know how it got there.
"There is nothing out there that should be obviously making
gamma rays," Dave Dixon, a physicist at the University of
California-Riverside, said in a statement. "These gamma rays
are providing the first evidence that some high energy
process is occurring out there."
The halo may be thousands of light-years thick -- a light-
year is about 6 trillion miles -- and could extend all the
way around the Milky Way, Dixon and his colleagues reported.
The phenomenon was mapped by NASA's orbiting Compton Gamma
Ray Observatory. The observatory looks at the universe
through gamma rays, which are highly energetic particles
invisible to Earth-based instruments because the atmosphere
absorbs them.
Gamma rays are photons, or particles of light, that have the
highest levels of energy of all forms of radiation. A single
gamma ray photon in the galactic halo has one billion times
the energy of a photon of ordinary visible light.
Astronomers study gamma rays because they might give clues to
the most violent events in the universe, such as the birth of
galaxies or the death of stars.
The discovery was made by Dixon and colleagues Dieter
Hartmann, of Clemson University, and Eric Kolaczyk of the
University of Chicago, and presented at a meeting of the High
Energy Astrophysics Division of the American Astronomical
Society in Estes Park, Colorado.
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